1. Field of the Invention
This invention relates to a method of making a spark plug electrode in which a spark-erosion resistant noble metal is secured to a firing portion of an electrode blank.
2. Description of Prior Art
In a spark plug for an internal combustion engine, it has been suggested that a noble metal tip is laser-welded to a curved or flat-shaped firing end of an electrode so as to increase a spark-erosion resistant property.
However, the laser beams causes to spherically swell the metal tip from the base of the firing portion. The swollen portion of the noble metal tip differes in height and position depending on the spark plug produced. For this reason, the noble metal tip comes to oppose another electrode out of normal place so as to change a spark gap interval, thus making it difficult to discharge the spark along the spark GaP. At the same time, the swollen portion of the noble metal tip interferes with an insulator when the electrode is placed within the insulator.
Therefore, it is one of the objects of the invention to provide a method of making a spark plug electrode in which a noble metal material is placed in a recess of a firing portion, and melted by means of laser beams only so as to form a noble metal portion, and thus maintaining the noble metal portion substantially in flush with the firing portion without protracting out of the recess, and contributing to an extended service life with relatively low cost.